This invention relates to cyanoacrylate adhesive compositions particularly intended for bonding glass.
It is known that xe2x80x9cinstantxe2x80x9d adhesives based on cyanoacrylate esters, while they are effective bonding agents for a wide variety of materials, do not give a permanent bond in joints involving glass. A strong bond to glass is obtained initially but generally the joint fails after a period of weeks or months at room temperature (RT) conditions. This major deficiency of cyanoacrylate adhesives is not fully understood. While this invention is not limited by-any theory, the deficiency is likely to be related to the extremely rapid speed at which these adhesives cure on glass aided by the basic nature of the surface. High stresses are generated in the bond line immediately adjacent to the glass, at a molecular level. These stresses make the polymer in the bond line uniquely susceptible to chemical or physical degradation, for example as a response to contraction and expansion of the joint with changes in RT or to hydrolytic attack by atmospheric moisture.
This major limitation of cyanoacrylate adhesives has persisted for over four decades since the materials were originally invented. Commercially available cyanoacrylate products are generally precluded from use in bonding glass particularly glass to glass bonds.
Kol""tsova et al, abstract of.Russian patent SU 1564172 describes a method of bonding cut glass by treating the surface to be joined with 20% of a 1:1 PhMexe2x80x94Me2CO solution of a Si-epoxy-containing oligomer, drying and then applying the adhesive (alpha-cyanoacrylate), and subsequently contacting the surfaces. The method described uses a two-part system.
JP 06100838 describes adhesives containing alpha-cyanoacrylates and an organosilicon compounds specifically Ph2SiH2.
GB 1,529,105 discloses cyanoacrylate based adhesives for glass and steel containing alpha-cyanoacrylates, 20% to 60% by weight of the composition of a plasticizer which is miscible with the ester and from 0.015% to 0.15% by weight of the composition of a carboxylic acid which is soluble in the ester. The adhesive is designed so as to be easily debonded when desired.
JP 52076344-A describes the pretreatment of substrates by application of organo-silane compounds of the formula Rxe2x80x94Si(X)3 where R is alkyl, alkenyl, allyl, aralkyl, cycloalkyl or cycloalkenyl group with 1 to 18 carbon atoms inclusive of those substituted by halogen, ether, OH, ester, epoxy and other groups. X is OCH3, OC2H5, OC3H7, OC4H5, OH, Cl, Br, I, Oxe2x80x94C(O)xe2x80x94CH3. The pretreatment process is said to eliminate the disadvantages of alpha-cyanoacrylate based adhesives observed when applied on glass, iron and ceramics, of deterioration on weathering, water resistance and impact resistance.
GB 1,430,506 describes an adhesive composition containing N,Nxe2x80x2-substituted bis-maleimide, alpha-cyanoacrylate and optionally containing a silane coupling agent or a diamine. The adhesive can be used to bond metal, glass, ceramic and heat resistant films and to produce resin laminations and flexible dielectric films.
GB 1 373 559 describes the use of an alkoxy or acyloxy silane in or with a cyanoacrylate adhesive composition for glass-glass or glass-rubber bonding. However the majority of the examples describe the use of the silane as a primer. Although a one-part composition is also described, there is no suggestion of including a plasticizer in it.
SU 1,328,361-A discloses a two-part cyanoacrylate adhesive system using silane derivatives which may be used in glass-glass bonding.
EPO 151,527 discloses cyanoacrylate adhesive compositions which employ calixarene compounds as additives and which give substantially reduced fixture and cure times on wood and other deactivating surfaces such as leather, ceramic, plastics and metals with chromate treated or ceramic oxide surfaces. Fumed silica fillers treated with polydialkylsiloxanes or trialkylsilanes may be employed as fillers. Plasticizers are optionally included. No mention is made of glass bonding.
U.S. Pat. No. 4,906,317 describes cyanoacrylate compositions which employ silacrown compounds as additives to give substantially reduced fixture and cure times on wood and other deactivating surfaces such as leather, ceramic, plastics and metals with chromate treated or acidic oxide surfaces. No mention is made of glass bonding.
The silacrowns of U.S. Pat. No. 4,906,317 are not silanes within the meaning of the term silane as used herein. As stated the silacrowns are prepared by transesterification of alkoxysilanes with polyethylene glycols i.e. they are reaction products of silanes but are not themselves silanes. Furthermore they do not act as free silanes. Silacrowns function as accelerators in the composition of U.S. Pat. No. 4,906,317. The silanes of the present invention act as coupling agents, a function which a silacrown does not perform.
The specific silacrowns disclosed in U.S. Pat. No. 4,906,317 and which are represented by the following formula do not function as silanes: 
wherein R2 and R3 are organo groups which do not themselves cause polymerisation of the cyanoacrylate monomer, R4 is H or CH3 and n is an integer. Examples of suitable R2 and R3 groups are straight chain or branched chain alkyl groups having 1 to 12 carbon atoms (which may be substituted with a substituent such as a halogen atom or an alkoxy group) a straight chain or branched chain alkenyl group having 2 to 12 carbon atoms, a straight chain or branched chain alkynyl group having 2 to 12 carbon atoms, a cycloalkyl group, an aralkyl group or an aryl group, alkoxy groups such as methoxy, and aryloxy groups such as phenoxy. The R2 and R3 groups may contain halogen or other substituents, an example being trifluoropropyl. Groups not suitable as R2 and R3 groups are basic groups such as amino, substituted amino and alkylamino.
U.S. Pat. No. 4,906,317 discloses the optional inclusion of fumed silicas treated with polydialkylsiloxanes or trialkoxyalkylsilanes. The fumed silicas are used as thickeners. The purpose of the silane which is retained on the surface of the silica is to maintain the fumed silica in a dispersion within the composition.
Fumed silicas are referred to in EP-A-0 209 067 also. Again the fumed silica is treated with trialkoxyalkysilane.
The present Applicants understand that trialkoxytrialkyl silane present in the compositions of U.S. Pat. No. 4,906,317, EP-A-0 209 067 and EP-A-0151 527 is chemically bound and immobilized on the surface of the silica in accordance with the function to retain the silica in a dispersed phase. It is not a xe2x80x9cfreexe2x80x9d silane in that it is not a mobile component of the composition. It does not function independently of the silica in the composition. In addition, it is not free to act as a conventional coupling agent and in particular does not act as a silane coupling agent or adhesion promoter. A coupling agent or adhesion promoter acts at the interface of the adhesive and the substrate being bonded to provide a better bond between the adhesive and the substrate.
While the EP ""067 patent also mentions the optional inclusion of plasticisers the object is to provide stable cyanoacrylate compositions with good thixotropic properties. It is not directed to the problem of glass bonding.
EP-A-0 137 849 relates to an alpha-cyanoacrylate-based instant adhesive composition containing benzophenonetetracarboxylic acid or its anhydride, and optionally plasticisers. A heat resistant composition is sought. No reference to the problem solved by the present invention, namely cyanoacrylate glass bonding is made in this document.
While the constituents mentioned herein are well known individually as polymer modifiers or adhesion promoters, their particular combination and use in this invention are unique, and the benefits gained in effectively bonding glass are unexpected. For example the compositions disclosed in GB 1,529,105 contain high levels of phthalate plasticizer in ethyl cyanoacrylate but the resulting adhesives are claimed to be suitable only for temporary bonding purposes on glass or steel. Two-part adhesive systems where silanes are employed to pretreat glass are described in Japanese Patent JP 5207634. The inconvenience of a two-part system is overcome by the one-part adhesive composition of the present invention.
It would be desirable to provide cyanoacrylate based adhesive compositions that overcome the deficiencies and limitations described above and gives strong durable adhesive bonds on glass, including crystal glass. It would also be desirable to provide one-part glass-bonding adhesive compositions, which are stable on storage and are also effective adhesives for bonding a wide range of other materials.
The present invention meets those desires by providing a one-part adhesive composition including (a) a cyanoacrylate monomer; (b) at least one plasticizer in the amount of 15 to 60% w/w by weight of the composition; and (c) at least one silane in the amount of 0.01% to 5.0% w/w by weight of the composition.